In a typical cellular wireless network, the area covered by the network is divided into a number of cells. Each cell is served by a base transceiver station which transmits signals to and receives signals from terminals located in the respective cell associated with a particular base transceiver station. The terminals may be mobile stations which are able to move between cells.
Management of the radio resources (and any other network resource) is normally done in a distributed way in the current networks. In particular, it is the responsibility of the controller of a base station to control the resources of its own base station. In the GSM (Global System for Mobile Communications) standard, a base station controller (BSC) is arranged to control a set of base stations. In the proposed third generation system using CDMA (Code Division Multiple Access), a radio network controller (RNC) is arranged to control the resources of its own base stations. In the CDMA system, the base station is sometimes referred to as Node B. However in this document the term base station will be used. The controllers in both of these systems are arranged to control a number of base stations. However the number of base stations which are controlled are relatively small. Accordingly, with this approach the efficiency of any resource management function or algorithm is limited by the fact that the coordination of the usage of the resource is possible only within the controller's own limited resources.
A further problem is that the algorithms used by the controllers use information received via the existing interfaces of the controller, and the possibility of transferring new information or measurements is restricted. This would require either the modification of the existing standard interfaces or the provision of new interfaces. It would not be practical to implement this on all of the controllers of a network.
The problems described previously will become more relevant in the future. This is because in the newly designed network architectures, most of the radio resource control functions are moved from the controllers, such as the radio network controller and the base station controller, to the base station in order to allow the implementation of a more efficient real time RT algorithm. One example of a function which can be advantageously be done in the base station rather than in the base station controller is channel assignment. An example of such an architecture is that proposed for IP RAN (internet protocol radio access network). This means that the area controlled by the controlling entity is reduced from the base station controller or radio network control area (which encompasses the area covered by a number of base stations) to only the coverage area of a single base station.
The limitations of the radio controller boundaries also have particular relevance when a network operator owns more than one radio access system (for example a CDMA system and a GSM system) with a common coverage area. This is because there is a need for a common management and coordination of the allocation of resources of the different system so that multimode terminals can be controlled to use the optimum one of the access systems. A multimode terminal is able to access both access systems. The use of controllers such as base station controllers, radio network controllers or base stations themselves will not permit the advantages of multimode terminals to be fully realised. The number of network operators who will use more than one radio access system is expected to increase drastically, given current developments. In addition to third generation systems such as CDMA, other systems such as Wireless LAN (local area network), IS-41 (a US version of CDMA), etc are being developed.
A distributed management of the resources, such as currently used, has a further disadvantage in that it does not allow overall control of the Quality of Service offered to the end user. This is because the distributed resource managers have control of only part of the resources that has an impact on the quality of service for an end user.
Distributed management of the resources, such as in the known systems, also has limitations in terms of operability. This is because the introduction of new features and the changing of existing parameters has to be done by accessing each one of the distributed control entities (for example the radio network controller, the base station controller or base station). The different entities may be provided by different manufacturers and so have different user interfaces.
There is a further problem with the arrangement described previously. In particular, in a network, the handover decision (i.e. the decision if and to which cell the handover shall be performed for a terminal) is based on terminal measurements and other mobile station specific information as well as some static handover parameter and target cell information set via operation and maintenance (this latter parameter is normally originated by radio network planning tools). This handover mechanism has the following drawback. The handover decision cannot take into account the dynamic information of all of the target cells unless all of them are controlled by the same controller. The dynamic information may be for example the cell load, the channel availability, the interference level, or the like. In the case of handover from one radio access system to another, the candidate target cells are controlled by different controllers. The handover decision cannot be taken based on dynamic parameters unknown to the controller, such as load of other network elements, transport load, CN (Core network) load or the like.